1. Field of the invention
The present application relates to an over-current protection device, and more particularly to a surface-mountable over-current protection device and the method of making the same.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Over-current protection devices are used for protecting circuitries from damage resulted from over-heat or over-current. An over-current protection device usually contains two electrodes and a resistive material disposed therebetween. The resistive material has positive temperature coefficient (PTC) characteristic that the resistance thereof remains extremely low at room temperature and instantaneously increases to thousand times when the temperature reaches a critical temperature or the circuit has over-current, so as to suppress over-current and protect the cell OF the circuit device. When the resistive material gets back to the room temperature or over-current no longer exists, the over-current protection device returns to be of low resistance and as a consequence the circuitry again operate normally. In view of the reusable property, the PTC over-current protection devices can replace traditional fuses, and have been widely applied to high density circuits.
Electronic apparatuses are being made smaller as time goes on. Therefore, it has to extremely restrict the sizes or thicknesses of active and passive devices. Surface mountable over-current protection devices usually use an insulating adhesive material layer, such as FR-4 or the like used in print circuit board (PCB) manufacturing., to support device rigidity. To acquire good adhesive strength between the PTC material layer and the insulating adhesive material layer, the resin content of the insulating adhesive material layer has to be taken into account. For large resin content, the insulating adhesive material layer is usually thicker and the adhesive force for jointing with the PTC material layer increases. However, the entire thickness of the device will increase significantly. For a small resin content, the insulating adhesive material layer is thinner and as a result that the entire thickness of the device can be diminished. However, the adhesive strength between the insulating adhesive material layer and the PTC material layer and the production yield will decrease. For instance, the over-current protection device containing a single PTC device usually has a thickness larger than 0.8 mm, and the over-current protection device containing two PTC devices connected in parallel has a thickness larger than 1.2 mm.
Accordingly, simultaneous achievements of good adhesive strength and thinning the device are unobtainable; therefore current devices cannot meet the demands of portable apparatuses at present